suitable management of rivers

suitable management of rivers

1. How rivers are used

   • A source of water
     • Irrigation and water supply
   • A source of water power
     • Hydroelectricity or watermils
   • A waste outlet
     • used as a drain taking effluent out to sea
   • A routway
     • roads and ril links follow valleys, river traffic and shipping
   • A source of food
     • Fish makes up the main source of protein in many LEDCs

2. Sustainable

   • They meet our needs today as well as meeting the needs of future generations

3. Flood

   • A temporary excesses of water that cover areas that are normally dry

4. Causes of flooding

   • Physical
     • Heavy rainfall
       • More water going into river
       • Excessive surface run-off
       • Flash Flood
     • Impermeable rocks
       • rain water can't percolate into the groundwater, so it flows quickly into the river by through flow and surface run-off
       • reduces infiltration into the ground meaning percipitation is more likely to be taken to the river as surface run-off
   • Human
     • Urbanisation
       • water can't soak into the ground because the new surfaces are impermeable
       • the water goes straight into the river through surface run-off and through drains
       • more tarmac and concrete creates impermeable surfaces
     • deforestration
       • Less root support for soil
       • less water used by plant
       • Big raindrops no longer broken up by leaves
       • the soil can get washed into the river
       • Takes up space, so there is less space for water
       • Deforestation also means the rain gets to the surface of the ground faster without trees, so the ground is more likely to get saturated

5. The river Derwent

   • yorshire
   • March 1999
   • 1.5 m deep
   • Causes of the flood
     • physical
       • Steep slopes, underlain with shale, near the source of the river Derwent transferred the water quickly to the channel
       • Heavy rainfall
         • Between 28 Febuary and 11 March over 250 mm of rain fell on the North York moors
       • Lack of infiltration
         • the rainfall fell on the ground that was almost saturated from previous rainfall events
       • Time of year
         • There was snow melt adding to the discharhe from the North York moor source region
     • Human
       • Deforestation meant the water reached the ground straight away instead of being intercepted so the soil was saturated more quickly
       • In Malton
         • rubbish blocked the channel making the flood worse than it should have been in this area
       • Peat removal
         • the extraction of peat in the source lowered the soil storage capacity there, as peat acts like a sponge
       • Building of a new housing estate at Malton meant more impermeable surfaces which reduced infiltration and increased surface run-off

6. The impact of flooding

   • on people
     • positive
       • replenishes drinking water supplies, especially wells
       • Provides sediments (other terms are silt or alliuvium) that naturally fertillises the soils of the floodplain
       • Countries such as Bangledesh and Egypt rely on floods
     • Negative
       • spreads waterborne disease
       • People and animals can be made homeless or even drown
       • Buildings and infrastructure (road and railways) can be damaged or destroyed
       • Crops grown on fertile floodplains can be washed away in flash flood
   • on the environment
     • Positive
       • Fish benefit as they can bread in the standing floodwater
       • In dry areas, floods bring relief from draught, providing drinking water for wild animals
     • negative
       • Flooding can wash chemicals or sewage into local rivers and so pollute them
       • Wild animals may drawn or lose their habitat during the flood

7. River management strategies

   • Soft engineering
     • Plant trees (afforestation)
       • In upper course
     • Plant water-loving plants
       • on the floodplain to to soak up water and lower the water tabloe
     • Enlarge existing natural leeves, or create embankments set back from the river
       • This still allows some natural flooding onto the floodplain
     • Land use Zoning
       • When the land has different building controls depending on how far away from the river it is. Areas most likely to be flooded are protected from urban development.
       • E.g those closest to the river- no building, next land zone- low risk housing.
     • Washlands
       • these are parts of the river floodplain in the lower course into which the river can flood temporarily
       • There are one kind of flood storage area and are usually sports pitches or nature reserves
       • People are not allowed to build on them
   • Hard engineering
     • Building dams or reservoirs in the upper course
       • These trap and store water, then let it out in a controlled way
       • Reservoirs can be used for leisure and hydro- electricity, but can flood good farm land, displace people and destroy habitats.
       • they are very expensive
     • Building high concrete embankments/ leeves along the sides of the river to contain any floodplain
     • Flood walls can be built around settlements and important factories or roads
       • They're quite expensive and don't look very natural
       • However, they are pretty effective
     • Storage areas
       • water can be pumped out of the river and stored in temporary lakes
       • Then it is pumped back in after the water level in the river has gone down.
       • These are very effective but fairly costly and sparse land is needed to pump the water into
     • Changing the river channel
       • deepening and widening increasing CSA, allowing it to contain more water, meaning discharge needs to be greater to create a river
       • Straightening the river (channelisation)
         • this makes the water move faster through this section of the river, so it doesn't build up and is less likely to flood
       • This totally changes the ecosystem in the river and spoils the natural meanders
       • Also further downstream where the river is channelised, water can build up and flood there